Editing Potter sequence (section)

==Pathogenesis==
Development of the mature [[kidney]] begins between weeks 5 and 7 of [[gestation]]. Fetal urine production begins in early gestation and comprises the majority of the [[amniotic fluid]] in the second and third [[Pregnancy#Physiology|trimesters]] of pregnancy. The fetus continuously swallows amniotic fluid, which is reabsorbed by the gastrointestinal tract and then reintroduced into the amniotic cavity by the kidneys via urination. [[Oligohydramnios]] occurs if the volume of amniotic fluid is less than normal for the corresponding period of gestation. The fetal urine is critical to the proper development of the lungs by aiding in the expansion of the airways ([[Pulmonary alveolus|alveoli]]) by means of hydrodynamic pressure and by also supplying [[proline]] which is a critical [[amino acid]] for lung development. Alveoli are the small sacs in the lungs that exchange oxygen with the blood. If the alveoli, and thereby the lungs, are underdeveloped at the time of birth the infant will not be able to breathe air properly and will go into respiratory distress shortly after birth due to [[pulmonary hypoplasia]] (underdeveloped lungs). This is the primary cause of death to Potter sequence infants secondary to renal failure. The fetal urine also serves to cushion the fetus from being compressed by the mother's [[uterus]] as it grows.{{citation needed|date=April 2021}}